The present invention refers to a device for producing fibrous non-woven structures.
Various sectors of industry use non-woven fabrics of different thickness and conformation to cover, isolate and protect. For example, non-woven materials are used in the fields of clothing, furniture, car industry, civil engineering, and in all other fields where its use seems more convenient with respect to the traditional woven materials.
The fibrous structures, or non-woven webs, are generally produced through machines distributing fibers on a mobile surface that, once cohesive, form a compact structure with a constant thickness.
These well-known machines, used to obtain non-woven fabrics with a disordered structure, consist of a plurality of cylinders for carding the fibers and a fan, placed upstream the last carding cylinder, to convey an air flow in a duct having a "Venturi section".
The Venturi section is obtained through a metallic frame tangent to part of the lateral surface of the carding cylinder. The section sizes give the air flow, which runs through it, speed and pressure enough to free the fibers from the clothing of the carding cylinder and set them down onto a mobile surface placed downstream of said section. This surface is generally formed by a perforated drum or screen belt, which allows air to be drawn away.
These known machines present various drawbacks, both from a practical and economical point of view. Further, they do not complete the production cycle of non-woven webs.
In fact, the fiber cohesion is generally made by other machines using solutions of glue and water sprayed on the fibrous structure.
This reinforcement method, which is applied after the structure is formed using a fluid different from air, alters the fibers distribution on the mobile surface, thus comprising the final homogeneity of the product.
Another drawback of these known machines is that the carding cylinder, and its fastening and transmission mechanisms, undergo an unavoidable obstruction of dust and fibers due to the air flow. For these reasons, this kind of machine needs particular structures and materials, as well as an accurate and complex manufacturing.
Another drawback of some of these machines is that they produce non-woven fabrics only in certain weights or thicknesses, and can be varied only by overlapping different layers.
Other machines are know, which use compressed air flows downstream of a Venturi section and create a high depression on the carding cylinder at the same level of the section itself. This depression frees fibers from the cylinder and distributes them on the underlying surface.
Another great drawback of these machines is that the compressed air flows are generated by constant sections, and cannot be varied in their intensity. On the other hand, the possibility of increasing or decreasing the air volume and speed according to the kind of fibers and the final product thickness, allows for a sensible improvement in the fibers distribution on the mobile surface to obtain a more homogenous non-woven fabric.
Another drawback of these machines is that the ducts for compressed air flows are subjected to very high pressure. As a result manufacturers are compelled to use special materials for some parts of the machines. However, very high thickness are often required when common materials are used which may cause problems with respect to encumbrance and manufacturing of the machines.
Another drawback of these machines is that the particular building structure does not allow for easy maintenance operations, especially the cleaning of the Venturi section and of the other sections generating the air flows.